Some interesting things about these kinds of measaging platforms.
Many exhanges/algo/low-latency/hft firms have large clusters of these kinds of systems for trading. The open source stuff out there is kind of different from the typical systems that revolve around a central engine/sequencer (matching engine).
There's a large body of knowledge in the financial industry on building low-latency versions of these message processors. Here's some interesting possibilities. On an e5-2670 with 7122 solarflare cards running openonload, its possible to pump a decent 2M 100byte messages/sec with a packetization of around 200k pps.
Avergae latency through a carefully crafted system using efficient data structures and in-memory only stores can pump and process a message through in about 15 microseconds with the 99.9 percent median at around 20 micros. This is a message hitting a host, getting sent to an engine, then back to the host and back.
Using regular interrupt based processing and e1000s probably yields around 500k msgs/sec with average latency through the system at around 100 micros and 99.9% medians in the 30-40 millisecond range.
Its useful to see solarflares tuning guidelines on building uber-efficient memcache boxes that can handle something like 7-8M memcache requests/sec.